(Reuters) - A Texas man told authorities he carved a pentagram into the back of his 6-year-old son "because it is a holy day" in reference to the numerical date of 12-12-12, police said.

Brent Troy Bartel, 39, of the Fort Worth suburb of Richland Hills, was in jail Wednesday on a $500,000 bond, charged with aggravated assault of a family member with a deadly weapon.

Police officers responded to an emergency dispatch call shortly after midnight from a man who said, "I shed some innocent blood," according to an audio recording of the emergency 911 call, released by police.

When questioned by the dispatcher, the man said, "I inscribed a pentagram on my son."

When the dispatcher asked why, the man responded, "because it is a holy day," according to the recording. He then hung up.

Moments later, police received a call from the boy's mother at a neighbor's house, said Officer Sheena Parsons, Richland Hills police spokeswoman. The mother could be heard on that recording crying and asking for help.

Police arrived at the Bartel home and found the boy shirtless and shivering, with a large pentagram carved on his back. Officers also found a box cutter at the house, which is believed to have been used in the attack, police said.

The boy was taken to a Fort Worth hospital for treatment. His injuries were "not life threatening," Parsons said. Police and Child Protective Services were investigating the attack.

Wednesday was 12-12-12 - a date some considered significant because such a match of day, month and year will not occur again in this century.

The pentagram is a five-pointed star sometimes associated with Satanism.